From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1JtVir-0007pS-8w
	for qemu-devel@nongnu.org; Tue, 06 May 2008 18:33:21 -0400
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1JtVim-0007pG-OY
	for qemu-devel@nongnu.org; Tue, 06 May 2008 18:33:20 -0400
Received: from [199.232.76.173] (port=40375 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1JtVim-0007pC-I6
	for qemu-devel@nongnu.org; Tue, 06 May 2008 18:33:16 -0400
Received: from py-out-1112.google.com ([64.233.166.179])
	by monty-python.gnu.org with esmtp (Exim 4.60)
	(envelope-from <anthony@codemonkey.ws>) id 1JtVim-000211-Ej
	for qemu-devel@nongnu.org; Tue, 06 May 2008 18:33:16 -0400
Received: by py-out-1112.google.com with SMTP id u52so32570pyb.10
	for <qemu-devel@nongnu.org>; Tue, 06 May 2008 15:33:15 -0700 (PDT)
Message-ID: <4820DCA5.2000605@codemonkey.ws>
Date: Tue, 06 May 2008 17:33:09 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] [4367] Align file accesses with cache=off (Kevin
	Wolf,	Laurent Vivier)
References: <E1JtQwU-0004sC-E9@cvs.savannah.gnu.org>
	<4820D905.4020407@bellard.org>
In-Reply-To: <4820D905.4020407@bellard.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Reply-To: qemu-devel@nongnu.org
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: qemu-devel@nongnu.org

Fabrice Bellard wrote:
> A note: in order to avoid uncontrolled recursions, it is better to call
> the read/write AIO callback outside the aio_read/write (see
> bdrv_aio_read_em).
>
> Personally I would not trust the OS to correctly handle the mix of
> O_DIRECT and buffered operations, especially if the corresponding file
> regions intersect !
>   

Indeed, why not just allocate a temporary buffer and realign the access 
such that it's correct?  If that involves doing a read first then a 
write, so be it.

Messing with file flags is very dangerous as there may be a request 
in-flight already in a different thread.  I don't think this patch is 
safe at all.

Regards,

Anthony Liguori

> Fabrice.
>
> Blue Swirl wrote:
>   
>> Revision: 4367
>>           http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=4367
>> Author:   blueswir1
>> Date:     2008-05-06 17:26:59 +0000 (Tue, 06 May 2008)
>>
>> Log Message:
>> -----------
>> Align file accesses with cache=off (Kevin Wolf, Laurent Vivier)
>>
>> Modified Paths:
>> --------------
>>     trunk/block-raw-posix.c
>> [...]
>>     
>
>
>